Biological rules

A biological rule or biological law is a general idea or guideline that helps explain patterns we see in living things. Scientists create these rules to make sense of how plants and animals behave and where they live all around the world. These rules can apply to many different kinds of organisms, not just a few.

Biologists have been looking for these patterns since the very beginning of their science. Even Aristotle noticed some important rules about animals that give birth. For example, he saw that bigger animals usually have fewer babies and live longer, while smaller animals have more babies but don’t live as long. Elephants, which are big, have few babies and live a long time, while mice, which are small, have many babies but don’t live as long.

These rules help scientists organize what they learn from studying nature and can even help predict what they might find in the future. Some of the first well-known biological rules were created by scientists like Karl Ernst von Baer, who studied how embryos develop, and Constantin Wilhelm Lambert Gloger, who looked at how animals get their colors. Sometimes, scientists question how useful these rules really are, but they still help us understand the natural world better.

List of biological rules

Biological rules are simple ideas that help us understand patterns in living things. Scientists have noticed these patterns and given them names.

Here are some important biological rules:

• Allen's rule explains how animals in cold places have less exposed body area to stay warm, while animals in warm places have more exposed body area to stay cool.
• Bergmann's rule tells us that animals in colder places tend to be bigger, while animals in warmer places tend to be smaller.
• Cope's rule suggests that animals usually get bigger over time as they evolve.
• Deep-sea gigantism describes how deep-sea animals are often larger than their relatives in shallow water.
• Dollo's law of irreversibility states that animals cannot return to a past stage of development, even if conditions are similar to before.
• Eichler's rule shows that the variety of parasites depends on the variety of their hosts.
• Emery's rule explains that insect parasites are often closely related to the insects they live on.
• Foster's rule, also called the island rule, says that animals on islands can become either larger or smaller depending on what food is available.
• Gause's law or the competitive exclusion principle states that two species cannot live in the same place if they need the same food.
• Gloger's rule tells us that animals in humid places tend to have more color.
• Haldane's rule explains that when two species mix and only one group cannot have babies, it is usually the group with two different sex chromosomes.
• Hamilton's rule suggests that genes spread when the benefit to a friend is bigger than the cost to the person who helps.
• Harrison's rule states that parasites change size depending on the size of their hosts.
• Hennig's progression rule says that the most basic animals in a group are found in the place where that group first appeared.
• Jordan's rule shows that animals in warmer water have more parts like fins or scales.
• Kleiber's law states that the energy use of animals and plants depends on their size to the 3/4 power.
• Lack's principle suggests that birds have the number of babies they can care for with the food available.
• Rapoport's rule tells us that animals and plants in places closer to the equator live in smaller areas.
• Rensch's rule explains that in animals, the size difference between males and females changes with the overall size of the animal.
• Schmalhausen's law states that animals at the edge of what they can handle are more easily affected by other changes.
• Thorson's rule explains that sea animals near the equator have many small babies, while those farther away have fewer but bigger babies.
• Van Valen's law states that the chance of a species dying out is the same no matter how old it is.
• von Baer's laws tell us that baby animals start looking similar and become more different as they grow.
• Williston's law suggests that parts of an animal’s body often become fewer and more specialized.